Produced fluids from a hydrocarbon well include multiple components, the most common being gas, oil, water, and sand. It is common to store the produced fluids in one or more production tanks, where the components are allowed to at least partially separate. As the tank fills, it is necessary to draw off the fluids, such as by using a tank truck. As each component is treated separately, the tank truck is filled with one component at a time, and “mixed loads” are avoided whenever possible. Often there will be a water outlet toward the bottom of the tank, and an oil outlet that is a certain distance above the water outlet. This allows a tank truck to draw off either water or oil. However, as it may be difficult to tell what is being drawn off, or due to operator inattention, it is not uncommon for mixed loads to occur.